• Title/Summary/Keyword: Magnetic measurement

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Measurement and Statistical Analysis of Magnetic Fields Produced by Cloud Discharges (운방전에 의해 발생되는 자장의 계측과 통계적 분석)

  • Lee Bok-Hee;Gil Hyoung-.Jun;Cho Sung-Chul;Shim Eung-Bo;Woo Jung-Wook
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.54 no.6
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    • pp.262-268
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    • 2005
  • In this work, to obtain the detailed information about lightning electromagnetic field waveforms, the LabVIEW based-measurement system of time-changing magnetic fields was designed and constructed. The frequency bandwidth of the magnetic field measuring system ranges from 300 [Hz] to 1 [MHz], and the response sensitivity is 2.78 [mV/nT]. Data acquisition system with the resolution of 12 bits and memory capacity of 32 [Mbyte] was triggered by the magnetic field to be measured. The properties and parameters of the magnetic fields produced by cloud discharges were statistically investigated. The magnetic field waveforms radiated from cloud lighting discharges tend to be bipolar, with two or more narrow and several pulses superimposed on the initial front part. The recording length of the magnetic field measurement system is about 10 [ms]. The mean duration of cloud discharges is 1.3 [ms], and the number of outburst pulses for the period is 8 in average. The front times of the magnetic fields are 6.15 [$\mu$s] in average. The the zero-to-zero crossing times that is the initial half-cycle duration is widely dispersed and the mean value is 9.61 [$\mu$s], and the mean value of percentage depth of dip to opposite polarity is 41.1 [$\%$].

A Study on the MEG Imaging (MEG 영상진단 검사에 관한 연구)

  • Kim, Jong-Gyu
    • Korean Journal of Clinical Laboratory Science
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    • v.37 no.2
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    • pp.123-128
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    • 2005
  • Magnetoencephalography (MEG) is the measurement of the magnetic fields produced by electrical activity in the brain, usually conducted externally, using extremely sensitive devices such as Superconducting Quantum Interference Device (SQUID). MEG needs complex and expensive measurement settings. Because the magnetic signals emitted by the brain are on the order of a few femtoteslas (1 fT = 10-15T), shielding from external magnetic signals, including the Earth's magnetic field, is necessary. An appropriate magnetically shielded room is very expensive, and constitutes the bulk of the expense of an MEG system. MEG is a relatively new technique that promises good spatial resolution and extremely high temporal resolution, thus complementing other brain activity measurement techniques such as electroencephalography (EEG), positron emission tomography (PET), single-photon emission computed tomography (SPECT) and functional magnetic resonance imaging (fMRI). MEG combines functional information from magnetic field recordings with structural information from MRI. The clinical uses of MEG are in detecting and localizing epileptic form spiking activity in patients with epilepsy, and in localizing eloquent cortex for surgical planning in patients with brain tumors. Magnetoencephalography may be used alone or together with electroencephalography, for the measurement of spontaneous or evoked activity, and for research or clinical purposes.

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Measurement of Magnetic Field Generated by the Operations of Electric Appliance (전기기구의 운전에 의하여 발생되는 자계의 측정)

  • 이복희;길경석;박형기
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.43 no.6
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    • pp.1001-1009
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    • 1994
  • The present paper deals with a new developed sensor for measuring the time-varying magnetic fields and describes the experimental results of trasient magnetic field that takes place during the operations of electric appliance. The operation principle of the self-integrating magnetic field sensor by using coaxial cable is analyzed and a calibration investigation is carried out. The frequency bandwidth of the magnetic field measurement system is from 40 Hz to about 300 kHz. The magnetic field induced by the starting and/or operation of electric appliance mainly includes the odd harmonics such as the third, the fifth and the seventh harmonics. The magnetic field intensity caused during the operation of ultrasonic washer is inversely proportional to distance, this correspodns to induction component. As a result, it was known that the odd harmonics of magnetic field in the desing of electromagnetic shield employed for protecting electronic circuit and control devices have to be considered.

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A study on in-process measurement of hardening depth for LASER surface hardening process control (강재의 레이저 표면경화 공정제어를 위한 경화층깊이의 실시간 측정에 관한 연구)

  • 우현구;박영준;조형석;한유희
    • 제어로봇시스템학회:학술대회논문집
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    • 1991.10a
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    • pp.252-257
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    • 1991
  • This paper proposed that the eddy-current measurement method can be used a means of in-process measuring the hardening depth in Laser surface treatment process. Also, this paper deal with the numerical analysis of magnetic flux distribution and experimental result of measurement. In Laser heat treatment process of steels, a thin layer of the substrate is rapidly heated to austenitizing temperature and subsequently cooled at a very fast rate due to the self-quenching by heat conduction into the bulk body, to produce a martensite structure which have low magnetic permeability. The eddy-current measurement method depends on the properties of material to be measured such as electric conductivity, magnetic permeability and geometry. In this paper, the hardening depth was measured by detecting relevant magnetic permeability changes caused by heat treatment of steels.

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A Methodology of Finding the Direction of Lightning Discharge using Loop-type Magnetic Field Sensors (루프형 자계센서를 이용하여 뇌방전이 발생한 방향을 탐지하는 기법)

  • Lee, Bok-Hee;Cho, Chi-Youn;Cho, Sung-Chul
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.28 no.10
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    • pp.63-68
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    • 2014
  • This paper deals with a methodology that applies the time-varying magnetic fields produced by the cloud discharges to find the direction of thunderstorm movement. We investigated the basic performance of the magnetic field measurement system composed of multi-turn loop-type sensors, the differential amplifier and active integrator. As a result, the response characteristics of the magnetic field sensor system to sinusoidal signals was excellent. The frequency bandwidth ranges from about 1 kHz to 500 kHz, the response sensitivity was 0.16mV/nT. In addition, we proposed the algorithm that determines the direction of lightning discharges using the comparison of the output signals of right-angled loop-type magnetic field sensors. The accuracy of the direction finding of lightning discharges is fairly well within the measurement error of less than $5^{\circ}$. The magnetic field measurement system proposed in this work can be used to track the direction of thunderstorm movement.

Development of a HTS SQUID gradiometer system for the measurement of very weak magnetic field in an unshielded environment (비자기차폐환경에서 미세 자기장 측정을 위한 고온초전도 gradiometer 시스템의 개발)

  • Kim, In-Seon;Kim, Jin-Mok;Park, Yong-Ki
    • 한국초전도학회:학술대회논문집
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    • v.10
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    • pp.151-154
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    • 2000
  • We have developed a YBCO SQUID gradiometer system for the measurement of a very weak magnetic field in an unshielded environment. The system consists of a SQUID gradiometer sensor, low noise pre-amp, and FLL(fluxlocked loop) control electronics. The gradiometer sensors have been fabricated on STO bicrystal substrates, and exhibit a magnetic noise of 300 fT/${\surd}$ Hz/cm at 100 Hz. The overall magnetic field noise of the SQUID gradiometer system was about 10 pT/${\surd}$ Hz/cm at 10 Hz without any magnetic shield. The system demonstrated a high stability for a long time, and real-time measurement resolution ${\le}$ 100 pT/cm in the unshielded environments.

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Performance Analysis of Magnetic Torquer for Spacecraft Control

  • Lee, Seon-Ho;Seo, Hyun-Ho;Rhee, Seung-Wu
    • 제어로봇시스템학회:학술대회논문집
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    • 2005.06a
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    • pp.1313-1317
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    • 2005
  • This paper presents the overall design, manufacture, and test result of the high capacity (more than 150 Am^2) magnetic torquer for the use of satellite control. To provide an electrical current to the magnetic torquer, the driving electronics is also constructed. The integration and test of the magnetic torquer and its driving electronics are performed via the magnetic field measurement according to the distance and the magnetic torque measurement with torque-meter. To compare the performance obtained from the test results we also perform computer simulation with three-dimensional model.

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Magnetic levitation properties of single- and multi-grain YBCO bulk superconductors

  • Kim, C.J.;Yang, A.Y.;Lee, S.H.;Jun, B.H.
    • Progress in Superconductivity and Cryogenics
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    • v.24 no.3
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    • pp.52-56
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    • 2022
  • Single-grain (c-normal or c-parallel) and multi-grain YBCO superconductors were prepared by a melt growth process with/without seeding. The magnetic levitation force and trapped magnetic field at liquid N2 temperature (77 K) of the YBCO superconductors were investigated. Samples for the levitation force measurement were zero-field cooled (ZFC) to 77 K, and samples for trapped field measurement were field-cooled (FC) using Nd magnets. As for the magnetic levitation force, the c-normal, single grain sample showed the largest value, whereas the multi-grain sample showed the lowest value. The trapped magnetic field of the c-normal and c-parallel single-grain samples was 4-5 times that of the multi-grain sample. In addition, as the external magnetic field (the number of magnets) increased, the both properties increased proportionally. These results were explained in terms of the orientation dependence of the levitation forces and the magnetic field trapping capability of the YBCO superconductor.

A Study on the Difference Method of Magnetic Resonance Signal Measurement when Using Multi-channel Coil and Parallel Imaging

  • Choi, Kwan-Woo;Lee, Ho-Beom;Son, Soon-Yong;Jeong, Mi-Ae
    • Journal of Magnetics
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    • v.22 no.2
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    • pp.220-226
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    • 2017
  • SNR (signal to ratio) is a criterion for providing objective information for evaluating the performance of a magnetic resonance imaging device, and is an important measurement standard for evaluating the quality of MR (Magnetic Resonance) image. The purpose of our study is to evaluate the correct SNR measurement for multi-channel coil and parallel imaging. As a result of research, we found that both T1 and T2 weighted images show the narrowest confidence interval of the method recommended by NEMA (The National Electrical manufacturers Association) 1 having a single measurement method, whereas the ACR (American College of Radiology) measurement method using a multi-channel coil and a parallel imaging technique shows the widest confidence interval. There is a significance in that we quantitatively verified the inaccurate problems of a signal to noise ratio using a ACR measurement method when using a multi-channel coil and a parallel imaging technique of which method does not satisfy the preconditions that researchers could overlook.

Yoke Topology Optimization of the Bias Magnetic System in a Magnetostrictive Sensor (자기변형 센서 바이어스 자기계의 요크 위상최적설계)

  • Kim, Yoon-Young;Kim, Woo-Chul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.923-929
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    • 2004
  • A magnetostrictive sensor is a sensor measuring elastic waves. Because of its unique non-contact measurement feature, the sensor receives more attentions in recent years. These sensors have been mainly used to measure longitudinal and torsional waves in ferromagnetic waveguides, but there increases an interest in using the sensor for flexural wave measurement. Since the performance of the sensor is strongly influenced by the applied bias magnetic field distribution, the design of the bias magnetic system providing the desired magnetic field is critical. The motivation of this investigation is to design a bias magnetic system consisting of electromagnets and yokes and the specific objective is to formulate the design problem as a bias yoke topology optimization. For the formulation, we employ linear magnetic behavior and examine the optimized results for electromagnets located at various locations. After completing the design optimization, we fabricate the prototype of the proposed bias magnetic system, and test its performance through flexural wave measurements.